House Extensions Rickmansworth
Single storey rear and double storey extensions in Rickmansworth, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Guide from £40,000 (London-derived)
- Free site survey, itemised quote
GS Renovation builds rear, side and wraparound extensions on houses in Rickmansworth. We appoint the structural engineer, build to their calculations, and coordinate the building control application and inspections from the foundations up. Fully insured, registered in England, company number 14611254, with free no obligation quotations and one point of contact on site.
For Rickmansworth, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Hertfordshire work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Rickmansworth: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Hertfordshire work generally runs below the London figures; your price follows a site visit. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Rickmansworth
Rickmansworth range: choose above
Which authority decides, and under which plan
The local planning authority for Rickmansworth is Three Rivers District Council, and planning enquiries go to 01923 776611 or dc.online@threerivers.gov.uk. The Batchworth Neighbourhood Plan 2023 to 2038 was made on 20 May 2025 and now forms part of the development plan used to decide planning applications in the area. It covers Eastbury, Moor Park and Rickmansworth within the Batchworth Community Council parish boundaries.
Policy BW DE1 of that plan requires new development to respond to the Batchworth Neighbourhood Design Code on building heights, materials, development frontages, plot widths, boundary treatments and street enclosure, and states that departures need full justification. A design that ignores the code is therefore not simply a question of taste. We are a contractor and not a planning consultant, so on anything borderline we would expect you to take architectural or planning advice before an application goes in.
Housing in Rickmansworth
The Council Tax list puts Rickmansworth at about 11,770 homes, 26% flats against 74% houses; 8% went up before 1919, 20% between the wars and 72% after 1945. A detached house in Rickmansworth often extends far enough from the boundary that no party wall notice is needed, and 35% of homes here are detached.
The design code has its own checklist for extensions
It asks specific questions, and they are worth reading before anything is drawn. The household extensions checklist in the Batchworth Neighbourhood Design Code asks whether the roof form of the extension is appropriate to the original dwelling, taking account of the angle of pitch. It asks whether a side extension retains important gaps within the street scene and avoids a terracing effect, and whether it is set back from the front of the house.
It also asks whether dormer roof extensions sit within the roof slope. On materials, the code states that alterations to existing buildings must use local materials, and that artificial materials imitating traditional ones should be avoided. It names yellow stock brick, red brick and white render as the building materials of the plan area. Matching brick and mortar to the original house is a sourcing decision we make early, because lead times on a genuine match run longer than people expect.
Moor Park sets measurable numbers, not just principles
The appraisal there gives figures you can check a sketch against. A minimum of 20 per cent of the site frontage at existing building lines must be kept clear of all development along the entire flank elevations. Not less than 1.5 metres is to be kept clear between flank walls and plot boundaries. Buildings including all outbuildings such as garages and car ports should not cover more than 15 per cent of the plot area.
That 15 per cent counts any first floor area overhanging the ground floor and any basement area built beyond the ground floor footprint. Construction in front of the existing building line or facade is unacceptable, and that includes replacement garages and porches over specified dimensions. The appraisal also states that flat roofs, and flat sections formed by truncating a pitched roof with an artificial ridge, are unacceptable in the conservation area. Those constraints shape the design before costing begins.
Ground conditions and the forms that go with an application
Foundations are designed to what is actually under the plot. British Geological Survey 1:50,000 mapping records the bedrock beneath Rickmansworth High Street and Station Road as the Lewes Nodular Chalk Formation. It records Alluvium, described as clay, silt, sand and gravel, over the chalk on the valley floor at the Rickmansworth Aquadrome, at Batchworth Lock and along the lower part of Cedars Avenue. Around Sandy Lodge Road in Moor Park the bedrock is the Lambeth Group, and under Main Avenue it is the Seaford Chalk Formation.
On paperwork, Three Rivers District Council requires a local biodiversity checklist with planning applications, alongside the application form and location plan, plus a Community Infrastructure Levy additional information form. The whole Batchworth plan area falls within a Mineral Safeguarding Area, so applications for non minerals development may not be determined until Hertfordshire County Council has had the chance to comment on whether the proposals would sterilise mineral resources. Build that into your expected decision time.
Kitchen extensions in Rickmansworth
77% of the houses in Rickmansworth are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in Rickmansworth; the build figures are in the table above.
Side return extensions in Rickmansworth
Side returns belong to Victorian and Edwardian terraces, and only 8% of homes in Rickmansworth predate 1919, so they are the exception here; most extensions run across the full rear width instead. Our side return extension page covers the build in detail, with build rates of £2,400 to £3,200 per m².
Double storey extensions in Rickmansworth
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Rickmansworth often needs planning permission from Three Rivers District Council. With 57% of homes here semi-detached or detached, the side of the house is often an option too. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Planning applications and permitted development assessments
- Bi-fold, sliding and French door openings to the garden
- Drawings and the structural engineer's design coordinated for you
VOA Council Tax stock of properties, March 2025, for Rickmansworth North & Loudwater, Rickmansworth West, Moor Park & Batchworth and Mill End, Heronsgate & Maple Cross. Counts rounded by the VOA.
Why Choose GS Renovation in Rickmansworth
An extension here is judged against the Batchworth Neighbourhood Plan and its design code, which became part of the development plan in May 2025, and departures from the code need full justification. GS Renovation builds to the engineer's calculations, coordinates building control from foundations to completion, and tells you where the design questions need an architect or planning consultant rather than a contractor. One point of contact on site throughout.
- Garden levels and access made good where the build meets outside
- Permitted development checked before you pay for a planning application
- Building control applications and inspections coordinated for you
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George is a very hard working builder, and has done a fantastic job on replacing my Bathroom. His attention to detail was great and I wouldn't…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
FAQ
Frequently Asked Questions about House Extensions Rickmansworth
What is included in your house extensions price in Rickmansworth?
A GS Renovation price for house extensions in Rickmansworth includes everything needed to finish the work and get it signed off, within £2,000 to £2,800 per m² for a rear extension (London-derived). That covers labour, materials, the engineer's design, a Hertfordshire Building Control inspection of the foundations before concrete is poured, and making good. Anything uncertain at the WD3 property is flagged before starting rather than added later.
Your Moor Park house already fills much of the plot width. Can you extend upwards instead?
Not where the building already covers 80 per cent or more of the plot width at the building line. The Moor Park appraisal states that further extension towards the boundaries or upwards will not be permitted in that situation. That threshold is measured at the building line, so a projecting bay or a flank garage can change the reading. Confirm the figure from a measured survey rather than an estate agent's plan before a design is commissioned.
Do you need a new crossover for access to a Moor Park plot?
If a new crossover is needed and it would affect a private road, a separate application goes to Moor Park (1958) Limited as well as to Hertfordshire Highways. Two consents, two timescales. Astons Road and Main Avenue are recorded as adopted highways in the 2004 Article 4 Direction, so check which category your road falls in. Start this alongside the planning application, because access for deliveries and for the finished driveway is the same question asked twice.
There is a mature tree where the extension would go. What notice does it need in Moor Park?
Six weeks written notice to the council before lopping, topping or felling a substantial tree. The Moor Park appraisal defines substantial as a trunk diameter of 75mm or more, measured 1.5 metres above ground level, which takes in far smaller trees than the word suggests. That six weeks sits in your programme whether or not the tree comes down. Foundation design near a tree you are keeping is a separate question for the engineer.
How deep will the foundations go on the gravel around Nightingale Road?
A trial hole decides it, not a rule of thumb. British Geological Survey mapping records the Winter Hill Gravel Member at Nightingale Road, a sand and gravel unit sitting over Seaford Chalk bedrock. The BGS Lexicon gives that gravel a recorded thickness of 1 to 8 metres, so the depth to bedrock is not a fixed number across a street. The engineer designs the foundation from what the hole shows, and building control inspects it open.
Your plot is east of Moor Park by the railway. Does the extension need a flood risk assessment?
Probably, because land to the east of Moor Park along the railway line lies within Flood Zone 3. The Batchworth Neighbourhood Plan notes that surface water flooding, linked to hard surfaces and drainage capacity, makes it worse. The Environment Agency also operates a flood warning area for the River Colne at Rickmansworth, reference 062FWF28Rickmans, covering Batchworth, Money Hill and Maple Cross. Confirm the zone for your own address with Three Rivers District Council before drawings are commissioned.
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